The Integrated Services Digital Network (ISDN) originated in 1967 is a communication network developed on the basis of the Integrated Digital Network (IDN). The ISDN supports end-to-end digital connections and various communication services, such as a telephone service, and provides standard user-network interfaces to be accessed by various terminals.
The Public Switched Telephone Network (PSTN), as a public communication network, provides voice and data communication services which are based on switched lines.
The PSTN/ISDN services generally refer to various services provided to users in the conventional PSTN/ISDN networks.
Conventionally, the PSTN/ISDN services are implemented in a circuit switched domain. With the fast development of the packet-based communication technologies, at present, the PSTN/ISDN services may also be implemented in a packet domain through the softswitch of a Next Generation Network (NGN).
There is a broad sense NGN and a narrow sense NGN.
The broad sense NGN generally refers to all the softswitch architectures in which bearer is separated from control, and the telecommunication service networks using broadband packets as bearer whether the network provides fixed services or mobile services to the users. The telecommunication service networks using broadband packets as bearer may be Internet Protocol (IP) networks or Asynchronous Transfer Mode (ATM) networks. Referring to the following definition of NGN given in the Telecommunication Standardization Sector of International Telecommunication Union (ITU-T) in February 2004, an NGN is a packet-based network, provides multiple services including the telecommunication service, and is capable of using multiple bandwidths and transmission techniques of abilities of Quality of Service (QoS) to implement separation of service functions from bottom-layer transmission techniques; the NGN allows an access of users to networks of different service providers and supports general mobility, which realizes consistent and continuous provision of services to users.
The narrow sense NGN refers to networks based on broadband packet bearer, providing C4/C5 services and IP multimedia services to the users accessing fixed networks. In embodiments of the present invention, the NGN refers to a “narrow sense NGN” unless otherwise mentioned.
In a fixed NGN, the softswitch serves as a call processing node in the network, implementing the PSTN/ISDN services. A PSTN user or an ISDN user accesses the softswitch through access devices, such as an Audio Gateway (AG) and an Integrated Access Device (IAD), the softswitch implements the session control, the service control, and the functions of storing and managing user data, and thus the PSTN/ISDN services are provided to the PSTN user or the ISDN user.
In a technical solution implemented through the softswitch, the functions of call control and service control are coupled to one network node and implemented in the network node, which results in poor flexibility and is unfavourable to fast deployment and extension of services.
Furthermore, modification of a function may bring about changes of other functions, increasing the potential risk. And deployment and extension of some services will even lead to the upgrading of the whole network node, resulting in a high cost. The softswitch can be accessed by fixed terminals through various access devices, such as access devices based on different protocols including the AG and the IAD, and the implementation of the PSTN/ISDN services is related to the access of the users.
Besides the implementation of the PSTN/ISDN services, the softswitch also needs to provide the Service Switch Point (SSP) function to trigger an intelligent service. And the PSTN/ISDN services and the intelligent service conflict with each other because there is no unified trigger mechanism.
The PSTN/ISDN services are distributed and implemented in call processing nodes in the NGN, thus the call processing nodes may not cooperate with each other to implement the PSTN/ISDN services. And there is no definite service arbitrating point when a service conflict occurs.
Since the PSTN/ISDN services are distributed and implemented in the call processing nodes in the NGN, each service needs to be implemented repeatedly in all the softswitches in the network when a unified service brand is popularized, leading to the high cost of service popularization.
The PSTN/ISDN services are distributed and implemented in the call processing nodes in the NGN, it is difficult for the PSTN/ISDN services to function as a basic network service ability, i.e., as a shared network component, to cooperate with other services in the NGN to provide combined value-added services.
The user data are distributed in the call processing nodes in the NGN and the users could only acquire services at access points of the users, thus it is difficult to acquire the same services as previous services if the terminals of the users are allowed to move, and the popularization of the unified service brand is also limited.
The call processing nodes in the NGN may not share the user data of the users accessing the NGN owing to the distribution of the user data, and it is thus difficult to provide a cross call processing node service (a wide area service).
There is also a system with the function similar to that of the fixed NGN above in a Third Generation (3G) mobile telecommunication network, which is an Internet Protocol Multimedia Subsystem (IMS).
The IMS is an IP multimedia subsystem in a Wideband Code Division Multiple Access (WCDMA) network defined in the 3rd Generation Partnership Project (3GPP) R5/R6 standard and is a target network in the 3G mobile telecommunication network for implementing packet voice and packet data and providing unified multimedia services and applications. The IMS uses an IP packet domain as its bearer channel of signalling control and media transmission, uses the (SIP) as signalling of the call control, and achieves separation of service management, session control and bearer accessing. FIG. 1 shows network architecture of the IMS in the 3GPP R5/R6 standard. Refer to “3GPP TS 23.002” for detailed descriptions of each network entity and related interfaces in the IMS.
Although the IMS provides a mechanism for separation of the service management, the session control and the bearer accessing, a PSTN user and an ISDN user may not access the IMS through a visited domain node defined by the IMS standard because the IMS standard is put forward initially for a 3G mobile system, requires the terminal to support an access control protocol of the IMS (typically the SIP) and does not support the access management of the PSTN user and the ISDN user.